The mechanisms and dynamics of effective immunity versus specific immunosuppression will be investigated in various tumor-host-systems. Differential responses in vitro and in vivo of strain-specific, methylcholanthrene-induced rat tumors to defined antibodies and lymphocytes will be evaluated quantitatively. Purified, soluble tumor-associated antigen fractions will be prepared along with specific IgM, IgG and IgA antibodies so antigen alone, antibodies alone, and defined antigen-antibody complexes may be tested for immunizing versus blocking activities. Parallel studies with the well-known Sarcoma I system in congenic mice will be pursued. Pioneering studies of tumorigenesis and tumor immunity in primitive fish (sharks and hagfish) and advanced invertebrates (tunicates and echinoderms) will be undertaken to gain phylogenetic perspective on immunosurveillance against cancer. BIBLIOGRAPHIC REFERENCES: Characteristics of histocompatibility barriers in congenic strains of mice. J.L. Cantrell, N. Kaliss, & W.H. Hildemann, Transplantation, 19,95, 1975. Characteristics of specific unresponsiveness toward kidney and skin allografts in adult rats inoculated at birth with allogeneic bone marrow or kidney cells across a strong H-1 barrier. Y. Mullen & W. H. Hildemann, Transplantation, 20, 281, 1975.